Excess insulin responses to glucose load have recently been reported in patients with syndrome X (effort angina, ischemic-appearing ST responses to exercise, normal coronary arteries). To assess the prevalence in vascular effects of hyerinsulenemia in non-diabetic patients with chest pain syndromes and angiographically normal coronary arteries, we measured plasma insulin levels in 65 patients and 16 healthy controls of similar age, gender and weight. In a subset of 34 patients and controls, forearm vascular resistance was measured by impedance plethysmography. Although fasting insulin levels were similar for the patients with chest pain and angiographically normal coronary arteries and controls, patients had significantly higher peak insulin responses (153/-+77 vs 87/-+40 (mu)U/ml, p>0.01) to glucose 75 gm. Baseline and 5 minute post-ischemic forearm vascular resistances were similar for controls in patients both before and after glucose load despite hyperinsulemneia in the patients with chest pain and angiographically normal coronary arteries. Among the patients with chest pain and normal coronary arteries there was no correlation between the presence and severity of hyperinsulenemia, and the presence of hypertension, coronary microvascular dysfunction microvascular constrictor response to ergonovine) or EKG responses to exercise. Thus, although hyperinsulenemia is common in patients with chest pain regardless of the EKG response to exercise, the impact of increased insulin levels on the coronary and systemic vasculature is unclear.